My Solution to the Internship Challenge (Python code)

python/solution.py

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+# Intership Challenge Solution (6/28/2024)
+# Code written by Bralyn Loach-Perry
+
+def preprocess_input(input_text):
+    # Remove spaces and convert to uppercase
+    input_text = input_text.replace(" ", "").upper()
+    # Replace 'J' with 'I' (standard Playfair Cipher treatment)
+    input_text = input_text.replace("J", "I")
+    # Split input into digraphs (pairs of characters)
+    digraphs = []
+    i = 0
+    while i < len(input_text):
+        if i == len(input_text) - 1 or input_text[i] == input_text[i + 1]:
+            # Skip inserting 'X' for consecutive identical characters
+            i += 1
+        else:
+            digraphs.append(input_text[i] + input_text[i + 1])
+            i += 2
+    return digraphs
+
+def create_key_square(key):
+    # Create a list of unique characters in the key (without 'J')
+    key = key.upper().replace(" ", "").replace("J", "I")
+    key_set = []
+    for char in key:
+        if char not in key_set:
+            key_set.append(char)
+
+    # Create key square (5x5 matrix)
+    alphabet = "ABCDEFGHIKLMNOPQRSTUVWXYZ"  # without 'J'
+    key_square = []
+    for char in key_set:
+        if char not in key_square:
+            key_square.append(char)
+    for char in alphabet:
+        if char not in key_square:
+            key_square.append(char)
+    return key_square
+
+def find_position(key_square, char):
+    # Find position of a character in the key square
+    index = key_square.index(char)
+    row = index // 5
+    col = index % 5
+    return (row, col)
+
+def decrypt_digraph(key_square, digraph):
+    # Decrypt a digraph based on Playfair Cipher rules
+    (char1, char2) = digraph[0], digraph[1]
+    (row1, col1) = find_position(key_square, char1)
+    (row2, col2) = find_position(key_square, char2)
+
+    if row1 == row2:
+        decrypted_pair = key_square[row1 * 5 + (col1 - 1) % 5] + key_square[row2 * 5 + (col2 - 1) % 5]
+    elif col1 == col2:
+        decrypted_pair = key_square[((row1 - 1) % 5) * 5 + col1] + key_square[((row2 - 1) % 5) * 5 + col2]
+    else:
+        decrypted_pair = key_square[row1 * 5 + col2] + key_square[row2 * 5 + col1]
+
+    # Remove any 'X' that might have been added during encryption
+    if 'X' in decrypted_pair:
+        decrypted_pair = decrypted_pair.replace('X', '')
+
+    return decrypted_pair
+
+def decrypt_message(ciphertext, key):
+    # Preprocess input and create key square
+    digraphs = preprocess_input(ciphertext)
+    key_square = create_key_square(key)
+
+    # Decrypt each digraph and concatenate results
+    decrypted_message = ""
+    for digraph in digraphs:
+        decrypted_message += decrypt_digraph(key_square, digraph)
+
+    return decrypted_message
+
+ciphertext = "IKEWENENXLNQLPZSLERUMRHEERYBOFNEINCHCV"
+key = "SUPERSPY"
+
+# Decrypt the message using provided ciphertext and key
+plaintext = decrypt_message(ciphertext, key)
+print(plaintext)